The field of the invention relates generally to gas turbine engines and, more particularly, to center fuel nozzles used within gas turbine engines.
At least some known gas turbine engines ignite a fuel-air mixture in a combustor to generate a combustion gas stream that is channeled to a turbine via a hot gas path. Compressed air is channeled to the combustor by a compressor. Combustor assemblies typically use fuel nozzles that facilitate fuel and air delivery to a combustion region of the combustor. The turbine converts the thermal energy of the combustion gas stream to mechanical energy that rotates a turbine shaft. The output of the turbine may be used to power a machine, for example, an electric generator or a pump.
Known fuel nozzle assemblies include a flange that extends from an end cover that serves as the structural base of the fuel nozzle. A premix tube extends from the flange and is coupled to a swirler. The natural frequency of the fuel nozzle assemblies are generally a function of both the shape and length of the flange and premix tube combination. Moreover, in known fuel nozzle assemblies, the operating frequency of the gas turbine engine may produce low cycle and/or high cycle fatigue in fuel nozzle components and joints, such as for example, the flange, the premix tube, and/or the swirler, and/or joints defined between the components. Moreover, in known fuel nozzle assemblies, stress concentrations around the fuel nozzle assembly and/or an increase in structural break-out into the fuel holes as a result of the fuel nozzle assembly may develop if the natural frequency is similar to, or substantially the same as, the operating rotor frequency (including first through fourth multiple of rotor frequency), combustion tones and siren tones of the gas turbine engine.
Many known fuel nozzle assemblies use a variety of components that are manufactured from a variety of materials and that are coupled together with welded and brazed joints, such as along the joints defined between the flange, the premix tube and/or the swirler. Because of the different material properties, the different components may have different thermal growth rates and/or magnitudes of thermal expansion and contraction. Additionally, over time, the welded and brazed joints may be prone to fatigue, cracking, or premature failure during operation when exposed to the operating frequencies produced by the gas turbine engine.